1. Field of the Invention
This invention relates to a manufacturing method of a BGA (Ball Grid Array) type semiconductor device which has ball-shaped conductive terminals.
2. Description of the Related Art
A CSP (Chip Size Package) receives attention in recent years as a three-dimensional mounting technology as well as a new packaging technology. The CSP means a small package having about the same outside dimensions as those of a semiconductor die packaged in it.
The BGA type semiconductor device has been known as a kind of CSP. A plurality of ball-shaped conductive terminals made of metal such as solder is arrayed in a grid pattern on one principal surface of a package of the BGA type semiconductor device and is electrically connected with the semiconductor die mounted on the other side of the package.
When the BGA type semiconductor device is mounted into electronic equipment, the semiconductor die and external circuit on a printed circuit board are electrically connected by compression bonding of each of the conductive terminals to each of wiring patterns on the printed circuit board.
Such a BGA type semiconductor device has advantages in providing a large number of conductive terminals and in size reduction over other CSP type semiconductor devices such as an SOP (Small Outline Package) and a QFP (Quad Flat Package), which have lead pins protruding from their sides. The BGA type semiconductor device is used as an image sensor chip for a digital camera incorporated into a mobile telephone, for example.
FIGS. 11A and 11B show outline structure of a conventional BGA type semiconductor device. FIG. 11A is an oblique perspective figure showing a top side of the BGA type semiconductor device. And FIG. 11B is an oblique perspective figure showing a back side of the BGA type semiconductor device.
A semiconductor die 104 is sealed between a first glass substrate 102 and a second glass substrate 103 through epoxy resins 105a and 105b in the BGA type semiconductor device 101. A plurality of conductive terminals 106 is arrayed in a grid pattern on a principal surface of the second glass substrate 103, that is, on a back surface of the BGA type semiconductor device 101. The conductive terminals 106 are connected to the semiconductor die 104 through a plurality of second wirings 110. The plurality of second wirings 110 is connected with aluminum first wirings pulled out from inside of the semiconductor die 104, making each of the conductive terminals 106 electrically connected with the semiconductor die 104.
More detailed explanation on a cross-sectional structure of the BGA type semiconductor device 101 will be given hereafter referring to FIG. 12. FIG. 12 shows a cross-sectional view of the BGA type semiconductor devices 101 divided along dicing lines into individual dice.
The first wiring 107 is provided on an insulation film 108 on a top surface of the semiconductor die 104. The semiconductor die 104 is bonded to the first glass substrate 102 with the resin 105a. A back surface of the semiconductor die 104 is bonded to the second glass substrate 103 with the resin 105b. 
One end of the first wiring 107 is connected to the second wiring 110. The second wiring 110 extends from the end of the first wiring 107 to a surface of the second glass substrate 103. The ball-shaped conductive terminal 106 is formed on the second wiring 110 extended onto the second glass substrate 103.
A protection film 111 of an organic resin is formed before dicing on a top surface of the BGA type semiconductor device 101 described above, which has a V-shaped groove VG (Refer to FIG. 13A.). Conventionally, the protection film 111 is formed on a surface of the second wiring 110 by facing up the back surface of the semiconductor die 104, potting a thermosetting organic resin on it and spinning a semiconductor wafer, in which the semiconductor dice 104 are formed, to spread the thermosetting organic resin on the back surface utilizing centrifugal force.
In this method, however, the thermosetting organic resin accumulates too thick in a bottom of the V-shaped groove VG around the dicing line (dashed line), as shown in FIG. 13A. It is because the thermosetting organic resin has a property of a sticky paste. As a result, the organic resin accumulated in the bottom of the V-shaped groove VG shrinks more than the organic resin covering other portion of the semiconductor device 101, when the protection film 111 is hardened by baking (heat treatment). There arises a problem that the larger shrinking in the bottom of the V-shaped groove VG causes a warping in the semiconductor wafer. (The warping in direction indicated by arrows in FIG. 13B is caused.)
The warping in the semiconductor wafer poses a problem to a manufacturing process that follows. Especially in a process step to form the conductive terminal 106 by screen printing using the protection film 111 as a mask, accuracy of printing alignment gets worse, resulting in reduced yield or potential deterioration in reliability of the BGA type semiconductor device 101.